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"The genes for homosexuality have not been identified yet, despite a very significant effort," says Sergey Gavrilets, a professor at the University of Tennessee's National Institute for Mathematical and Biological Synthesis.

"When you put it together in one very coherent framework, (the theory) is very logical and is supported by mathematical modelling. It is an explanation that seems to be working much better than any existing explanations," says Gavrilets.

The model Gavrilets and his collaborators developed still needs to be tested with experiments looking for these triggers in DNA, he says.

Still, the new explanation into why homosexuality seems to run in families is encouraging to a lot of scientists, he says.

For decades, scientists have been searching for the "gay gene" - that definitive link that shows homosexuality is hereditary. The pursuit has yielded mixed results and little hard proof.

This new theory - which lies in a relatively new field of epigenetics - seems to be far more plausible, Gavrilets says.

It centres around epi-marks, an additional layer of information attached to our DNA that directs exactly how our genes are expressed. These epi-markers are typically freshly created with each generation, but new evidence shows they can be passed down from parents to the fetus, and can be influenced by things like diet and stress.

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When those epi-marks are passed to the opposite-sex offspring - that is, from fathers to daughters or mothers to sons - it can lead to a sensitivity in testosterone.

"So now the daughter will have a high sensitivity to testosterone, and there's a high probability of her being masculinised," Gavrilets says.

"And if a mother passes this epi-mark to her son, he will inherit low sensitivity."

The study, which was published online on Tuesday in The Quarterly Review of Biology, has generated interest from other scientists who want to test the theory, Gavrilets says.

"There's a lot of excitement in the field, and everyone has been asking about this fresh view on this very old problem.

"We may still be wrong, but this is how science works. We formulate a certain hypothesis and people prove if it's right or wrong."

Even if his theory is proved true, Gavrilets says epigenetics may be only part of the equation when it comes to a person's sexual preference. Environmental and cultural factors may still contribute to a person's lifestyle, he says.